Emulsion and blended ANFO-emulsion explosives constitute the majority of explosives used in the mining industry. These types of explosives require sensitisation prior to detonation by the introduction of void spaces into the emulsion matrix. Void spaces create hotspots within the explosive sensitising it to detonation. The density of a typical emulsion explosive is around 1,300 kg m−3 and this density needs to be reduced to around 1,000 kg m−3 for an efficient blast. As such, gas is introduced into the emulsion equivalent to around one third of the total emulsion density. This gas may be introduced, for example, by sparging air through the emulsion or blending in hollow glass micro balloons or porous material.
A more effective means of sensitisation is through chemical gassing, where a chemical reaction is used to generate gas bubbles within the emulsion. Chemical gassing usually involves the reaction of nitrite with ammonia or other amine substrate such as thiourea to produce nitrogen gas. However, such processes are typically slow, especially at low to ambient temperatures, which can cause significant mine-site delays.